In recent years, there has been a concern for depletion of fossil fuel such as petroleum or coal, and expectation for sustainably-usable renewable energy has been rising. As the renewable energy, a solar cell, wind power generation, and the like can be cited. Because these depend on weather and a natural situation in a power generation amount, there is a problem that stable supply of electric power is difficult. Therefore, there has been made an attempt to store the electric power generated by the renewable energy in a storage battery and stabilize the electric power. However, when the electric power is stored, there are problems that a cost is required for the storage battery and a loss occurs at a time of storage.
For such points, attention is being given to a technology of performing water electrolysis using the electric power generated by the renewable energy to produce hydrogen (H2) from water or reducing carbon dioxide (CO2) electrochemically to convert it into a chemical substance (chemical energy) such as a carbon compound such as carbon monoxide (CO), a formic acid (HCOOH), methanol (CH3OH), methane (CH4), an acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), or ethylene (C2H4). When these chemical substances are stored in a cylinder or a tank, as compared with when the electric power (electric energy) is stored in the storage battery, there are advantages that a storage cost of energy can be reduced and a storage loss is also small.
As a carbon dioxide electrolytic device, for example, a structure in which a cathode solution and CO2 gas are brought in contact with a cathode and an anode solution is brought in contact with an anode is being studied. As a specific configuration of the electrolytic device, for example, there can be cited a configuration which includes a cathode solution flow path disposed along one surface of the cathode, a CO2 gas flow path disposed along the other surface of the cathode, an anode solution flow path disposed along one surface of an anode, and a separator disposed between the cathode solution flow path and the anode solution flow path. When a reaction to, for example, produce CO from CO2 is performed for a long time by using the electrolytic device having such a configuration and, for example, passing a constant current through the cathode and the anode, there is a problem that a deterioration over time of a cell output such as a decrease in a production amount of CO or an increase in a cell voltage occurs. Therefore, a carbon dioxide electrolytic device which makes it possible to suppress the deterioration over time of the cell output is required.